Industry is lacking a composition such as fluidized bed catalyst or additive contact solids for economically removing sulfur oxides from emissions from a variety of industrial processes. Further, the industry lacks effective and economical methods for using a fluidized bed of particles to remove sulfur oxides from emissions.
Synthetic hydrotalcites, known as layered double hydroxides, are useful as contact solids in numerous industrial processes. In view of a limited supply of naturally-occurring hydrotalcite, various efforts have been made to achieve a reasonably economic alternative material in the form of synthetic Layered Double Hydroxides `LDH`!.
Production of analogous crystalline materials has been fruitful, and it may be expected that important new uses for the class of hydrotalcite crystalline solids will increase industrial demand.
The `hydrotalcite-like` materials of Schutz et al (U.S. Pat. Nos. 5,399,329 and 5,507,980) are characterized by crystals having very high broadness to thickness ratios in the 50:1 to 5000:1 range. These interesting materials have desirable mechanical and chemical properties, which will render them useful as solids binders or as active chemical sites. Recent efforts in this aspect of layer propagation have identified certain anionic species which contribute to forming the large sheets of synthetic hydrotalcites. The mechanism whereby these lower alkanoic acid anions direct the important plate shape is not understood; however, large plate crystals having a maximum dimension of about 5 to 500 microns (.mu.) impart excellent mechanical properties.
A structural description of the class of "brucite" crystals is found in the work of Pinnavaia et al (U.S. Pat. No. 5,358,701, incorporated by reference). Briefly, the metal oxide layers consist essentially of magnesium oxide (MgO) configured structurally with octahedral hydroxy groups. A trivalent metal oxide, such as alumina (Al.sub.2 O.sub.3), can be inserted into the brucite crystalline lattice in the octahedrally-coordinated metal oxide layer. In the case of natural hydrotalcite, the carbonate layer or gallery may be replaced by substitution of various acidic anions, sulfate, sulfite, nitric, etc.